The present invention is generally relating to a wafer treating technique after finishing integrated circuits on a wafer, particularly to a wafer treating method for making adhesive dies.
After manufacturing the integrated circuits on a semiconductor wafer, a plurality of dies are singulated from the semiconductor wafer and according to various packaging styles are attached on a proper IC substrate, or one of dies is attached one on top of the other die to form multi-chip stack. Die is attached onto a printed circuit board to form Ball Grid Array (BGA) package. Die is attached to die pad or inner leads of a lead frame to form Thin Small Outline Package (TSOP). Conventional adhesive for die-attaching is thermosetting silver liquid compound or solid polyimide adhesive tape, which is applied on base carrier (e.g., substrate, leadframe or lower die) during die-attaching.
A method for assembling multi-chip module disclosed from U.S. Pat. No. 2001/0005935 is to attach a larger die onto a substrate using a die attach machine, then a smaller die is affixed on the larger die without using a die attach machine. The adhesive attaching the larger die and the smaller die conventionally is a liquid thermosetting adhesive or solid polyimide tape. However, that is failed to disclose the procedure of coating the adhesive (firstly coated on the smaller die or on the larger die prior to die-attaching and the procedure of wire-bonding.On one hand, when a liquid thermosetting adhesive is used for die-attaching prior wire-bonding, it is difficult to pre-coat on the smaller die (upper die) and also easy to contaminate the bonding pads of the larger die (lower die) due to flowage of liquid thermosetting adhesive. On the other hand, when the liquid adhesive is printed after wire-bonding, the printing screen is unable to be placed on the larger die(or substrate) with bonding wires, so that adhesive must be applied on the larger die before wire-bonding. Thus, the limits for multi-chip packaging process are quite a lots, lead to package uneasily. Alternatively, a solid adhesive tape may also be used for die-attaching, but cost of adhesive tape is high and the adhesive tape is demanded double-sided adhesive for die-to-die, die-to-substrate or die-to-leadframe bonding. Conventionally the adhesive tape is firstly attached on a substrate (leadframe or larger die) in predetermined pattern, then a die is bonded on the adhesive tape. The dies do not have adhesive after sigulating from a wafer.
A first object of the present invention is to provide a wafer treating method for making adhesive dies by utilizing a liquid adhesive with two-stage property printed on a wafer. The printed adhesive with two-stage property is pre-cured to become solid without flowable and adhesive under room temperature (B-stage condition), then after singulating the wafer, a plurality of dies with B-stage adhesive will be obtained for decreasing cost of forming adhesive.
A second object of the present invention is to provide a wafer treating method for making adhesive dies by utilizing a liquid adhesive with two-stage property printed on a wafer. The adhesive with two-stage property is precured to become solid film without flowable and adhesive under room temperature (B-stage condition), then after singulating the wafer, the dies with B-stage adhesive will be obtained, so as to possess good processing characteristic for a variety of semiconductor packaging processes.
In accordance with the wafer treating method for making adhesive dies of the present invention, a semiconductor wafer having integrated circuits is provided. The wafer has a plane surface, such as an active surface or an inactive surface. A liquid adhesive with two-stage property is evenly coated on the partial or overall surface of the wafer by means of screen printing, stencil printing or spin coating. It is desirable to coat the liquid adhesive with two-stage property on the partial surface of the wafer without covering the cutting paths or bonding pads of the wafer. Next, the wafer is pre-cured to make the adhesive with two-stage property become a wafer-level thermo-bonding adhesive film with B-stage property, that is, being solid without flowable and adhesive under room temperature. Usually the pre-cured time is about 1 hour around 125xc2x0 C. Meanwhile, the B-stage solid film has thermosetting property and adhesion of thermal bonding, also has a glass transition temperature (Tg) more than 40xc2x0 C. for operation of positioning the wafer, sucking the dies utilizing a die binder and transportation after singulating the dies from the wafer. Thus the dies with wafer-level thermo-bonding adhesive film are provided to affix to a substrate, another die, a printed circuit board, a ceramic circuit board or a lead frame without extra adhesive. Therefore, the dies with wafer-level thermo-bonding adhesive film are able to be efficiently, broadly used in die-to-die stack or die-to-substrate attach for various packages at low cost.